The present invention relates to a super water-repellent coating film and to super water-repellent coating material to form the super water-repellent coating film. A super water-repellent coating film can be utilized for preventing snow covering, frosting, icing of surface, and the like. Practically, the super water-repellent coating material can be utilized in, for instance, treatment of an evaporator fin surface of an air conditioner for preventing the fin from frosting during a heating operation, or treatment of a parabolic antenna surface, for which the maintenance operation in winter is difficult because of heavy snow. Other practically applicable fields for a super water-repellent coating material are, for example, as a coating material for preventing icing of ships and aircraft, a coating material for the outer wall of houses, and a surface coating material for preventing water drop adhesion on the windshield of an automobile. Furthermore, for instance, the energy used to transport fluids in pipes can be reduced by super water-repellent treatment of the inner surface of a pipe used for aqueous solution transportation. Indeed, the field of application of super water-repellent coating films can be expected to expand more than ever in the future.
The super water-repellent phenomenon itself is not known generally, nor has there been any patent relating to a super water-repellent coating film. Although an introductory report on products using a super water-repellent coating film has been published in Nikkei Business, Feb. 13, 1995, no actual product in the form of a super water-repellent coating film has been commercialized. The reason is because technology to supply a large amount of super water-repellent coating film material at a reasonable price has not been established yet, and a super water-repellent coating film can not be obtained stably.
The super water-repellent phenomenon requires a contact angle of a solid body with water of at least 150 degrees. Under this condition, water forms water drops and moves on the surface of the solid body freely. When the contact angle is 180 degrees representing the maximum super water-repellent phenomenon, the contact area of the water drop and the solid body becomes zero. In the super water-repellent coating film, the surface profile of the coating film should be made fractal, or be formed so that the surface area per unit becomes indefinitely large, in addition to making the surface energy at the surface of the coating film low. In order to make the surface energy low, a fluorine group or silicon group surface treatment agent is generally used. However, the technology to form a surface profile having a fractal shape, or a surface profile having an indefinitely large surface area per unit, is difficult and hardly achieved. It is still uncertain in what range of sizes the surface is to be made fractal to effectively produce the super water-repellent phenomenon. Accordingly, the surface profile is difficult to form preferably. Especially, the surface of the coating film is difficult to form the by applying a coating material. However, if the super water-repellent coating film is formed by applying a coating material, utilization of the coating film can be extended widely, and a super water-repellent treatment of various surfaces will be available.
In view of these aspects of the super water-repellent technology, the inventor of the present invention has conducted research, and has found that a super water-repellent coating film can be obtained by forming a fractal shape at the surface of the coating film with a filler which is dispersed in the coating material, so that the surface area per unit is made indefinitely large, and by concurrently fluorinating the surface of the coating film with a perfluoropolyoxyalkyl compound added to the coating material, resulting in the present invention.